This invention relates to novel polymers and the use of these polymers alone and in conjunction with other materials as photoresists. More particularly, this invention is directed to polymers having the formula: ##STR2## wherein R.sub.1 is R.sub.5 --(z).sub.p ; R.sub.5 is terminal reactive group --O--; z is isocyanate --O--; p is zero or 1, however p is zero when m is zero; P.sub.1 is an organic radical; m is zero or 1, however m is zero when n is 1; R.sub.2 is an organic radical; P.sub.2 is an organic radical; r is zero or 1, however r is zero only when m is zero and n is zero; R.sub.3 is an organic radical; n is zero or 1; R.sub.4 is --(v).sub.w --R.sub.6 ; v is --O-- isocyanate--; w is zero or 1, however, w is zero when m is zero; R.sub.6 is --O-- terminal reactive group; i is an integer from 2-6; and P.sub.4 is the residue from a polyhydroxy compound.
The essence of photoresist processes is the use of a material which after exposure to actinic radiation can be removed from certain parts of the circuit board blank, but not from other areas. The material must be capable of sharp resolution, i.e., it must be a material where the exposed areas and the unexposed areas are clearly and sharply defined. There must also be good adhesion of the cured material to the underlying metal in order that excess metal not be removed during the etching step.
Many polymers, such as those disclosed in U.S. Pat. No. 4,422,914, can be successfully used as photoresists. However, the above-identified essential properties of image quality, adhesion and strippability have been improved upon by the polymers of this invention.
It has previously been found desirable, for fast and efficient curing of such polymers to include with the system relatively large amounts of a photoinitiating component. Even in systems wherein these large amounts of photoinitiators are compatible, most of the photoinitiator will remain chemically unbonded in the final cured composition, producing deleterious effects on the properties of these cured materials. An additional drawback to the use of high levels of photoinitiators is the possibility of the occurrence of side reactions by the unbonded portions of the photoinitiators on exposure to actinic radiation.
Accordingly, it is a principal object of this invention to provide a polymer, which when used in a photopolymerizable composition as a photoresist, will produce a printed circuit board with sharp definition.
It is another object of this invention to provide such a polymer, which when used as a photoresist, can be removed in its uncured state by the use of an aqueous solution.
It is another object of this invention to provide such a polymer, which when used as a photoresist and cured, will have good adhesion to the underlying substrate of the circuit board.
It is another object of this invention to provide such a polymer, which when used as a photoresist and cured, is susceptable to stripping using alkaline solutions.
It is a further object of this invention to provide such a polymer which has a photoinitiating component incorporated into its backbone.